The Prosthetic Body

If we consider the OED definition of prosthesis as "an artificial replacement for a part of the body," it would seem logically impossible that the body itself could serve a prosthetic function. Yet this view of the body as prosthesis was precisely what René Descartes set forth in his meditations on human nature, which powerfully shaped the dualist commonplaces inherited by the Victorians. Descartes saw humanity as having a dual nature composed of an immaterial soul and a material body, but the two sides were not equally human. He aligned rationality and identity exclusively with the immaterial soul, describing the soul as "a substance whose whole essence or nature resides only in thinking ..., from entirely distinct from the body and ... even easier to know than the body; and would not stop being everything it is, even if the body were not to exist" (Discourse 29, original emphasis). He saw the body, on the other hand, as the instrument through which the soul operated in a material world—its avatar or supplement, as it were. Though dualistic conceptions of human nature go back at least as far as Plato, Descartes's seminal contribution was to posit the mechanism through which the rational soul and the material body interact. He located the point of contact in the brain's pineal gland: "when we desire to walk or to move our body or to move in our body in some special way, this desire causes the [pineal] gland to thrust the spirits towards the muscles which serve to bring about this result" ("Passions" 378).

Cartesian dualism, often called interactionism, proved to be profoundly influential as a model for the relation between soul and body. Its central conceit—what Gilbert Ryle has memorably called "the Ghost in the Machine" (15-16)—made intuitive sense, unlike more esoteric versions of dualism (Gottfried Leibniz's psycho-physical parallelism, for example), and thus the body as prosthesis became a familiar trope over the next few centuries. Theologians such as Bishop Joseph Butler (1692-1752) explicitly stated the parallel: "Our organs of sense and our limbs are certainly instruments, which the living persons ourselves make use of to perceive and move with" just as we would deploy "a microscope or a staff" (27). Like Descartes, Butler stressed the independence of the soul from the body and conjectured that, hypothetically speaking, a person could inhabit many different kinds of bodies: "It is as easy to conceive that we may exist out of bodies, as in them; that we might have animated bodies of any other organs and sense wholly different from these now given us" (22).

Interactionism also framed the study of human biology. For example, German physiologist Johannes Müller (1801-1858), whose empirical research traced physical sensations and motor impulses to the brain stem and sub-cortical areas, likened the action of the soul on the nerves to the action of a pianist on a piano: "The fibres of all the motor, cerebral, and spinal nerves may be imagined as spread out in the medulla oblongata, and exposed to the influence of the will like the keys of a piano-forte" (qtd. in Young 116-17). Müller and others, however, drew a line between the lower areas of the brain and the cerebral cortex; they believed that the latter was the site of a human being's immaterial aspects—from this cortical vantage point, they concluded, the soul directed the rest of the brain and body. The revolutionary findings of Gustav Fritsch, Eduard Hitzig, and David Ferrier in the 1870s, however, challenged the interactionist model by establishing conclusively that the cerebrum had the same properties as the rest of the brain, and, moreover, that one could account for the higher functions (thought, emotion, volition) through the physical processes of the cerebrum. As physiological explanations became more compelling, spiritual explanations, such as interactionism, seemed less necessary and less convincing. In his controversial 1874 lecture on animal automatism, T.H. Huxley reflected these shifts in perspective when he argued that "states of consciousness," far from controlling the body, were instead the epiphenomenal by-products of material changes in the...